It is known to use polyols and natural fat- and oil-based products as lubricants. For instance, U.S. Pat. No. 4,885,104 discloses metalworking lubricants composed of a reaction product of natural fat or oil, a polyol having from 5 to 15 carbon atoms and a dicarboxylic acid having from 2 to 36 carbon atoms. The natural fat of the composition may be canola oil.
A food grade lubricant is disclosed in U.S. Pat. No. 5,185,091. The lubricant is preferably composed of decaglycerol monostearate, a triglyceride of a medium chain saturated fatty acids (of 6 to 10 carbon atoms) and glycerol. The ingredients are melted and then kneaded under rapid cooling in order to produce a desired emulsion having a specific dropping point. This product is hydrophilic and substantially insoluble in triglyceride oils.
It is also known that polyglycerol esters can be used as lubricants, and find utility in the textile arts.
One drawback of vegetable oil-based or esterified lower molecular weight polyglycerol-based compounds as lubricants is their low viscosity profile, which limits their range of usefulness. The viscosity of vegetable oils may be increased in a variety of ways including bodying (i.e., a controlled oxidation), sulfurization (as disclosed in U.S. Pat. No. 4,885,104) and blending with synthetic oils. Another possibility is to use synthetic polyol esters of polyhydric alcohols such as pentaerythritol, neopentyl glycol and trimethylol propane in total or in combination with vegetable oils (see again, U.S. Pat. No. 4,885,104). Although biodegradable, such esters are still relatively low in viscosity and as such, are limited in utility. Higher viscosities may be achieved by using dibasic acids to increase molecular weight, but biodegradability suffers and the economic and environmental considerations for using such lubricants become increasing less attractive.
A second drawback as noted above is the insolubility of such products in functional fluids.
The applicant has found a simple solution for improving the viscosity profile and solubility of biodegradable functional fluids; this solution includes reacting polyglycerols with fatty acids, triglyceride oils or fats and/or blending the resultant esterified polyglycerols with natural fats and oils.